The manufacture of phenolic glycol ethers (also know as alkylene phenolic glycol ethers), e.g., propylene glycol phenyl ether (PPh) and/or ethylene glycol phenyl ether (EPh), is long known and practiced. U.S. Pat. No. 2,852,566 teaches a semi-batch process that uses an ion-exchange resin as a heterogeneous catalyst containing quaternary ammonium hydroxide groups, U.S. Pat. No. 3,642,911 describes a batch reaction system for preparing phenoxyethanol using excess ethylene oxide in presence of urea as catalyst. U.S. Pat. No. 3,525,773 describes a process similar to that of U.S. Pat. No. 3,642,911 except that its process uses ammonia or an amide as the catalyst. Other similar teachings include U.S. Pat. Nos. 3,644,534, 3,364,267 and 3,354,227 and U.S. 2004/0181099.
One common process for making phenolic glycol ether, e.g., PPh and/or EPh, is a batch process in which propylene oxide (PO) and/or ethylene oxide (EO) is reacted with phenol in the presence of sodium hydroxide (NaOH) which serves as a catalyst. The oxides are added continuously into a mixture of phenol and NaOH catalyst until the amount of residual phenol in the reactor effluent is less than 100 parts per million (ppm). In order to achieve low oxide (less than (<) 15 ppm EO and <400 ppm PO) concentration in the reactor effluent, a long residence time (e.g., greater than 10 hours) is necessary to complete the oxide conversion and this, in turn, imparts a low capacity (i.e., a poor production rate) to the process. Moreover, the long residence time and the oxide to phenol weight ratio of slightly (e.g., 5% excess oxide) greater than 1 employed to minimize unreacted phenol and oxide is such that a significant amount of higher homolog products, e.g., dipropylene glycol phenyl ether, and other impurities are produced. This, in turn, requires significant distillation effort to purify the EPh and PPh even if the reactor effluent is neutralized with an acid, e.g., phosphoric acid, to remove the NaOH catalyst in order to avoid, further reaction. In addition, filtration of the resulting salt, i.e., sodium phosphate, requires an intensive operation.
In those instances in which a significant amount of higher homolog is desired, e.g., diethylene or triethylene glycol phenyl ether, conventional practice is to recycle mono-product to react further with the oxides to produce the desired higher homolog products (in particular the di-product). However this lowers the productivity of the process as a larger reactor volume is needed to accommodate the longer reaction time, or it requires a larger capital investment so as to allow recycling of mono-products. Moreover, while a simple phenol drying unit may be sufficient for mono-product production, usually a more intense operation, e.g., two or more phenol drying units coupled in series, is necessary to remove water from phenol recycle in order to obtain the desired purity in glycol formation.
Accordingly, of interest to the manufacturers of EPh and PPh is an alternative process, ideally a continuous process, that will eliminate the need for catalyst neutralization, salt filtration, and the long residence time while at the same time improving the selectivity, and hence quality, of the product. Also of interest is the ability to affect the mono-/di-product ratio without having to recycle mono-product.